Heat recovery system of plant using heat pump

ABSTRACT

Disclosed is a heat recovery system of a plant using a heat pump that absorbs some heat energy wasted from a condenser of the plant. The heat recovery system is constructed such that water condensed by the condenser is supplied to a service water heater via condensate pumps. A heat pump is installed between the condensate pumps and the service water heater for receiving the condensed water and the coolant. Some of the condensed water and the coolant, having passed through the heat pump, are supplied to a coolant inlet port of the condenser, and the remaining portions are supplied to the service water heater. The condensed water supplied to the service water heater is heated by a three way valve through which service water heating steam is supplied. Some of the steam is directly recovered to the condenser via a combustion air heater.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat recovery system of a plant using a heat pump. More particularly, the present invention relates to a heat recovery system of a plant using a heat pump that is capable of absorbing some heat energy wasted from a condenser of the plant, thereby improving power generation efficiency of the plant.

2. Description of the Related Art

As is already well known, a heat pump is a kind of technology that is widely applicable to production equipment of an industrial field, including refrigerators and freezers. The heat pump performs effective heat exchange with a high coefficient of performance (COP). Therefore, the heat pump is capable of effectively absorbing heat energy from the atmosphere, rivers, or industrial equipment that generates waste heat. In the most cases, the heat pump is used for cooling purposes although the heat pump is used for heating purposes in some cases. With the recent increase of interest in energy efficiency, technology for improving heat efficiency simultaneously using cooling and heating functions is gradually increasing.

The present invention relates to a heat recovery system that is capable of partially absorbing a large amount of heat energy wasted from a condenser of a plant using such a heat pump, thereby improving efficiency of the plant.

Meanwhile, a heat efficiency improvement apparatus of a plant using a thermoelectric element is disclosed in Korean Patent Application No. 2009-58580, which has been filed in the name of the applicant of the present application. The disclosed apparatus has an advantage in that the thermoelectric element is used, and therefore, no mechanical drive parts are provided, thereby achieving easy and simple application and noise prevention. On the other hand, the disclosed apparatus has a disadvantage in that the COP of the apparatus is excessively sensitive to temperature difference and current ratio between a high temperature part and a low temperature part, and therefore, the increase of the COP is limited, whereby it is difficult to apply the apparatus to large-scale equipment.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems of the related art, and it is an object of the present invention to provide a heat recovery system of a plant using a heat pump that is applicable to a large-scale plant and, in addition, is capable of recovering some heat discharged from a condenser of the plant due to a coolant, thereby improving efficiency of the plant.

In accordance with the present invention, the above and other objects can be accomplished by the provision of a heat recovery system of a plant using a heat pump constructed such that water condensed by a condenser in which a coolant flows from a coolant inlet port to a coolant outlet port to condense steam into water is supplied to a service water heater via a plurality of condensate pumps, wherein a heat pump is installed between the condensate pumps and the service water heater for receiving the water condensed by the condenser and the coolant discharged from the condenser, some of the condensed water and the coolant, having passed through the heat pump, are supplied to the coolant inlet port of the condenser, while the remaining portions of the condensed water and the coolant are supplied to the service water heater, the condensed water supplied to the service water heater is heated by a three way valve through which service water heating steam is supplied, and some of the supplied steam is directly recovered to the condenser via a combustion air heater.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a construction view illustrating a heat recovery system of a plant using a heat pump according to a first embodiment of the present invention;

FIG. 2 is a view illustrating the flow of heat in the heat recovery system according to the first embodiment of the present invention shown in FIG. 1;

FIG. 3 is a construction view illustrating a heat recovery system of a plant using a heat pump according to a second embodiment of the present invention;

FIG. 4 is a construction view illustrating a heat recovery system of a plant using a heat pump according to a third embodiment of the present invention; and

FIG. 5(A) is a schematic view illustrating input and output of energy into and from respective components of a plant before a heat pump is applied to the plant, and FIG. 5(B) is schematic view illustrating input and output of energy into and from respective components of a plant after a heat pump of the present invention is applied to the plant.

DETAILED DESCRIPTION OF THE INVENTION

Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a construction view illustrating a heat recovery system of a plant using a heat pump according to a first embodiment of the present invention, and FIG. 2 is a view illustrating the flow of heat in the heat recovery system according to the first embodiment of the present invention shown in FIG. 1.

The heat recovery system of the plant is constructed such that water condensed by a condenser 1 in which a coolant flows from a coolant inlet port 1 a to a coolant outlet port 1 b to condense steam into water is supplied to a service water heater 3 via a plurality of condensate pumps 2. In this embodiment, a heat pump 4 is installed between the condensate pumps 2 and the service water heater 3 for receiving the water condensed by the condenser 1 and the coolant discharged from the condenser 1. The coolant, having passed through the heat pump 4, is supplied to the coolant inlet port 1 a of the condenser 1. The condensed water is supplied to the service water heater 3. The condensed water, supplied to the service water heater 3, is heated by a three way valve 5 through which service water heating steam is supplied. Some of the service water heating steam is condensed by a combustion air heater 6, and is then directly recovered to the condenser 1.

When the steam is condensed into water by the condenser 1, a large amount of heat energy is wasted. In this embodiment, some of the wasted heat energy is absorbed by the heat pump 4, and service water is heated by the absorbed heat energy. At this time, the amount of heat to heat the service water may be changed according to a coefficient of performance (COP) of the heat pump 4.

Recently commercially available heat pumps have COPs of about 2 to 10. When a heat source is sufficient, and a heating temperature is about 15° C., the heat pumps may have a COP of 9 (Products of McQuay).

When a heat pump having a COP of 9 is used, therefore, it is possible to heat service water with the amount of heat equivalent to nine times the amount of electric power supplied to the heat pump.

As the service water is previously heated, service water heating steam may be left over. The steam has a relatively high temperature (about 60° C. or higher). After being used to heat combustion air, the steam is recovered to the condenser 1. As a result, the amount of heat introduced into a boiler is increased without the additional increase of fuel, thereby improving the efficiency of the plant.

Meanwhile, FIG. 3 is a construction view illustrating a heat recovery system of a plant using a heat pump according to a second embodiment of the present invention. The heat recovery system according to the second embodiment is identical to the heat recovery system according to the first embodiment except that the heat pumps 4 use steam to be supplied to the condenser 1 as a direct heat source.

In a heat recovery system of a plant using a heat pump according to a third embodiment of the present invention as shown in FIG. 4, service water is not heated by heat recovered to the condenser 1 using the heat pump 4 but combustion air is directly heated by the recovered heat such that the heated combustion air is supplied to the boiler. At this time, it is necessary to increase temperature difference at the same amount of heat since air has a lower specific heat than water. When the temperature difference is too large, however, the COP of the heat pump is lowered. For this reason, it is expected that this embodiment exhibits a lower increase in efficiency of the plant than the previous embodiments in which the service water is heated.

FIGS. 5(A) and 5(B) are schematic views illustrating input and output of energy into and from respective components of a plant before and after a heat pump is applied to the plant, respectively.

For example, when the present invention is applied to a plant having a boiler efficiency of 90%, a turbine efficiency of 46%, and a generator efficiency of 94%, the efficiency improvement of the plant may be estimated as follows. Before the heat pump is applied to the plant as shown in FIG. 5(A), the total efficiency of the plant=boiler efficiency×turbine efficiency×generator efficiency=output/input=498.923/1282.051=38.916%. After the heat pump of the present invention is applied to the plant as shown in FIG. 5(B), on the other hand, the total efficiency of the plant=output/input=504.248/1282.051=39.331%. That is, an efficiency improvement of about 0.415% is achieved. Such efficiency improvement may save a considerably large amount of energy in a large-scale plant.

This is possible when the entirety of the amount of recovered heat is supplied to the boiler. For a plant in which an air preheater is already installed, loss of exhaust gas is increased due to the increase in temperature of the exhaust gas during heating of the combustion air, with the result that efficiency increase effect may be insignificant. In this case, it is necessary to directly recover heat from the exhaust gas, the temperature of which has been increased from about 117° C. to about 143° C., and to use the recovered heat in a predetermined process. The recovered heat may be used in the predetermined process as follows. In a district heating system, the recovered heat may be used to heat service water for district heating. In a heavy oil or light oil plant, the recovered heat may be used to preheat fuel, thereby improving efficiency of the plant.

As is apparent from the above description, in the heat recovery system of the plant using the heat pump according to the present invention, some of the heat discharged from the condenser due to the coolant is recovered to the heat pump, and the recovered heat is reused, with the result that efficiency of the plant is improved, thereby saving fuel and reducing the discharge of carbon dioxide and thermal waste water.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

DRAWINGS

FIG. 1

-   -   STEAM     -   TO SECOND SERVICE WATER HEATER     -   SERVICE WATER HEATING STEAM

FIG. 2

-   -   COOLANT     -   STEAM     -   HEATED COOLANT     -   SEAWATER     -   DISCHARGE OF SEAWATER     -   RECOVERY     -   CONDENSATE PUMPS     -   HEAT PUMP     -   SERVICE WATER HEATING STEAM     -   SERVICE WATER HEATER     -   SERVICE WATER     -   COMBUSTION AIR     -   COMBUSTION AIR HEATER     -   INTO BOILER FURNACE

FIG. 3

-   -   STEAM     -   SEAWATER     -   DISCHARGE OF SEAWATER     -   RECOVERY     -   RECOVERY     -   CONDENSATE PUMPS     -   HEAT PUMP     -   SERVICE WATER HEATING STEAM     -   SERVICE WATER HEATER     -   SERVICE WATER     -   COMBUSTION AIR     -   COMBUSTION AIR HEATER     -   INTO BOILER FURNACE

FIG. 4

-   -   COOLANT INLET PORT     -   STEAM     -   COOLANT OUTLET PORT     -   COMBUSTION AIR     -   TO BOILER     -   HEAT PUMP     -   CONDENSATE PUMPS     -   CONDENSED WATER     -   FIRST SERVICE WATER HEATER     -   ADDITION     -   TO SECOND SERVICE WATER HEATER

FIG. 5

-   -   (A) BEFORE APPLICATION OF HEAT PUMP     -   BOILER     -   TURBINE     -   GENERATOR     -   CONDENSER     -   (B) AFTER APPLICATION OF HEAT PUMP     -   BOILER     -   TURBINE     -   GENERATOR     -   POWER TRANSMISSION END     -   CONDENSER     -   HEAT PUMP 

1. A heat recovery system of a plant using a heat pump constructed such that water condensed by a condenser in which a coolant flows from a coolant inlet port to a coolant outlet port to condense steam into water is supplied to a service water heater via a plurality of condensate pumps, wherein the heat recovery system comprises a heat pump installed between the condensate pumps and the service water heater for receiving the water condensed by the condenser and the coolant discharged from the condenser, the coolant, having passed through the heat pump, is supplied to the coolant inlet port of the condenser, the condensed water is supplied to the service water heater and heated by a three way valve through which service water heating steam is supplied, and the service water heating steam, having passed through a combustion air heater, is directly supplied to the condenser.
 2. The heat recovery system according to claim 1, wherein the heat pump is constructed so as to recover heat by directly receiving steam from the condenser.
 3. The heat recovery system according to claim 1, wherein the heat pump is constructed so as to heat combustion air and supply the heated combustion air to a boiler.
 4. The heat recovery system according to claim 1, wherein the heat pump is constructed so as to recover heat energy from exhaust gas having increased temperature and to use the recovered heat energy to heat district heating water or a fuel system. 